1. Field of the Invention
This invention relates to V-ribbed power transmission belts and, more particularly, to a V-ribbed belt having multiple ribs exposed on each of the opposite sides thereof to allow the belt to drive/be driven on both sides.
2. Background Art
V-belts are commonly used in the automotive environment. In a single engine compartment, multiple belts may each be coupled to a plurality of components. For example, one belt can be trained around pulleys on the crank shaft, an alternator, and a fan. Another belt can be trained around pulleys on the crank shaft and a power steering unit. Still another belt can be trained around the crank shaft and a cooler, or the like.
Recently, automotive designers have striven to maximize the useable passenger space in the automobile, reduce its weight, and minimize fuel consumption. Much effort has been concentrated on reducing the size of the engine.
One conventional belt construction, used in the automotive environment, has V-shaped ribs extending in a lengthwise direction of the belt, which ribs are disposed on the inside of an adhesive rubber layer in which load carrying cords are embedded. The outside of the adhesive rubber layer is covered with one or more layers of rubber impregnated canvas.
This type of belt is commonly assembled in a serpentine path on an engine so that both the inside and outside surfaces effect driving of various engine components. As such, the belt is required to be highly flexible, to bend at relatively sharp angles, and run smoothly in this bent configuration.
In one exemplary system, as shown in FIG. 2 herein, a V-ribbed belt 10 is trained around a drive pulley 12 and follower pulleys 14, 16, 18, each of which is carried by a shaft on a separate engine component so that the inside surface 20 of the belt 10 operatively engages each of the pulleys 12, 14, 16, 18. The outside surface 22 of the belt 10 operatively engages an idler pulley 24, through which tension on the belt 10 can be adjusted, and another follower pulley 26, operatively engaged with another engine component.
The outer surface 28 of the pulley 26 and the outside surface 22 of the belt 10 are both flat. These engaging flat surfaces 22, 28 do not have the capability to transmit as large a force as can be accomplished with V-shaped engagement surfaces as those on the inside surface 20 of the belt 10 and the pulleys 12, 14, 16, 18. That is, there is no wedge effect realized from the engagement of the surfaces 22, 28. As a result, there may be excessive wear on the outside surface 22, as well as on the inside surface 20 of the belt 10, with the result being that the belt 10 slips, particularly when the tension thereon has been reduced. This condition makes the belt 10 ineffective in transmitting power in a heavily loaded system.
To overcome the above problem, it is known to utilize a double V-ribbed belt, as shown at 30 in FIG. 1. The belt 30 has a first plurality of laterally spaced, longitudinally extending, V-shaped ribs 32 exposed on one side thereof, and a second plurality of laterally spaced, longitudinally extending, V-shaped ribs 34 on the other side thereof. The ribs 32, 34 have the same pitch, height, and shape. The ribs 32, 34 are on opposite sides of an adhesive rubber layer 36 in which longitudinally extending, laterally spaced, load carrying cords 38 are embedded. One example of this type of double V-ribbed belt is shown in FIG. 4 of U.S. Pat. No. 2,728,239.
Use of a double V-ribbed belt, of the type as shown at 30 in FIG. 1, allows large forces to be transmitted through the belt 30. However, with this type of belt in the system described, a situation may occur wherein the belt, at the base of the ribs 32, 34 tears in a vertical direction. This tearing may be the result of foreign matter being in the grooves 40, 42 between adjacent ribs 32, 34, or a misaligmnent between the pulleys and belt 30.
Heretofore, no structure is known by the inventors for reinforcing the belt, of the type shown at 30 in FIG. 1, to prevent this tearing condition. Since the body of the belt between the bottoms of the grooves 40, 42 is relatively thin, it would be logical to thicken the adhesive rubber layer 36 to accommodate reinforcing members. However, the flexibility of the belt would be compromised by reason of the increased thickness of the adhesive rubber layer 36.
It is known to embed short, laterally extending fibers in both the inside and outside ribs on a double V-ribbed belt to effect reinforcement thereof. As shown in FIG. 4 of U.S. Pat. No. 2,728,239, short reinforcing fibers are mixed in the same concentration in both the inner and outer ribs. It has been found that with this type of double V-ribbed belt trained around a plurality of pulleys, as in the system shown in FIG. 2 herein, the wear resistance of the belt deteriorates significantly. Further, the flexibility of the belt is significantly diminished over that which it would be in the absence of the fibers.
This is particularly a problem on small diameter pulleys, such as those typically used for an engine alternator. One possible solution to this problem is to enlarge the diameter of the alternator pulleys so that the belt is not required to bend at such a severe angle. However, this is counterproductive, defeating the goal of reducing the overall size of the engine in the engine compartment.